With the advent of electronic radios which use automatic scanning techniques as described for example in U.S. Pat. No. 4,135,158 to Parmet issued Jan. 16, 1979, there has been created a need for on channel signal detection systems for detecting the broadcast frequency at which the radio should stop scanning. However, in the case of a strong adjacent channel station producing a signal it is possible for the second or adjacent channel station to be picked up by the detection system and the radio to stop scanning at the undesired frequency.
Various techniques are known for providing automatic scan circuits to stop or interupt scanning as described for example in U.S. Pat. No. 3,559,076 to Worcester which describes a circuit for scan prevention during brief signal fades. Also it is known to provide an automatic tuning receiver for a specific television signal or the like which uses a high Q resonant circuit tuned to the particular frequency which produces control pulses within the band pass of the intermediate amplifier as described in U.S. Pat. No. 2,898,400 to Parmet et al. However, none of the known detection systems provide the desired operation of preventing strong adjacent channel stations from causing a desired channel station to be missed in the scanning process as is accomplished by the instant invention.